Earth Day: 40 years later
Climate changes again threaten civilization

Published 10:00 pm, Friday, April 16, 2010

We are newcomers here. It is tempting to think of ourselves as being on Earth since the beginning.

But the beginning was hot, hammered by meteors and bathed in radiation. There was no life here for the first 800 million years.

And for two and a half billion years after, the only residents of Earth were bacteria.

In our current form, humans have only walked the Earth for 250,000 of its 4.7 billion years.

For most of that time, our existence was precarious. Our early ancestors ate what they could gather or hunt and their lives were short and unpredictable. Having no other choice, humans survived by adapting to their environment.

Our ancestors were too few and their lives too simple to wrap themselves in the protective cocoon of technology.

When the environment changed drastically people died in large numbers, at least once bringing our species to the edge of extinction.

Approximately 70,000 years ago a supervolcano erupted on the island of Sumatra, covering the Indian subcontinent with a thick layer of ash and drastically changing the climate worldwide.

Because of this event, the total human population was reduced to fewer than 10,000 individuals. From these lucky survivors we are all descended.

We are children of the Ice Ages. Our species appeared in Africa during the millennia when great ice sheets pushed forward and receded, again and again.

As the human population grew, we spread out in search of food and living space, eventually settling in every continent except Antarctica.

It was not until the most recent retreat of ice around 12,000 years ago that humans learned to domesticate plants and animals. Agriculture allowed us to settle down and store food for the bad times. Populations grew and societies became more complex.

As our technology advanced, our ability to manipulate our environment increased. This allowed us to live longer and more comfortable lives. We had more children and more of our children lived to have their own. Great civilizations rose and fell.

But history is littered with the remains of great civilizations that could not adapt quickly to a changing environment. The Old Kingdom of Egypt, builder of the Pyramids, is an example of a civilization that crashed in response to a major change in climate.

Like an individual organism, human civilization produces waste which can poison its environment.

Among the wastes of modern civilization are gases that trap heat in the atmosphere. These greenhouse gases have been demonstrated beyond reasonable doubt to have great and negative effects on long-term patterns in temperature and precipitation -- the climate on which our civilization depends.

Climate determines how much fresh water is available to us. Climate determines which plants and animals can live where we live, and which we can grow for food.

Throughout human history the climate has changed us. Until very recently, we have not had the power to change our climate. Now we do.

Earth Day reminds us -- those of us willing to be reminded -- that we are a part of the Earth's environment.

We are subject to its changes and are responsible for many of its changes ourselves.

Our ancestors relied on it absolutely. We now find ourselves modifying it profoundly.